Advances in polymerization technology have provided more efficient, highly productive and economically enhanced processes. Especially illustrative of these advances is the development of technology utilizing metallocene catalyst systems and other advanced metallocene-type catalyst systems. However, metallocene and metallocene-type catalysts typically exhibit high catalyst activity as soon as the catalyst is injected into the reaction system. Thus, the catalyst should be injected in more than one location in commercial-scale reactors to provide good distribution of catalyst in the reactor.
It is often useful to support various types of catalyst compounds, for example metallocene and metallocene-type catalyst compounds, on a carrier such as, for example, silica or alumina. The use of supported or heterogeneous catalyst systems increases process efficiencies by assuring that the forming polymeric particles achieve a shape and density that improves reactor operability and ease of handling. These supported catalyst systems are often suspended in solution to form a catalyst slurry composition, and the catalyst slurry composition is injected into the polymerization reactor through various catalyst injection systems.
Feeding supported slurry catalyst compositions can prove problematic for high activity catalysts, which may require low slurry catalyst composition flow rates. The equipment used to measure and control the flow rates of the slurry catalyst composition may have very small passages, which are prone to pluggage by agglomerates that occasionally form in the slurry catalyst composition. This is particularly problematic for control valves in the system that injects the slurry catalyst composition into the reaction system. These problems are exacerbated when an already small flow rate must be split into more than one injection point. The problems are exacerbated even further when it is desirable to distribute the slurry catalyst composition uniformly in the reactor, which requires the flow rate of the slurry catalyst composition be fairly uniform between each of the multiple catalyst injection points.
U.S. Pat. Nos. 6,606,675, 6,608,149, and 6,956,089 disclose a catalyst composition prepared by continuously combining a catalyst component slurry with a catalyst component solution to form a slurry catalyst composition, then introducing the slurry catalyst composition into an operating polymerization reactor. These patents also disclose systems for delivery of the slurry catalyst composition to the reaction system.
U.S. Pat. Nos. 5,317,036, 5,693,727, 6,075,101, 6,245,868, and 7,235,614 all describe various processes and techniques for introducing supported and unsupported catalyst compositions in liquid form to a polymerization reactor.
In view of the references described above, there exists a need to deliver a slurry catalyst composition to multiple feed points in a polymerization reactor that is not prone to plugging when attempting to control low flow rates of the slurry catalyst composition. Furthermore, there exists a need to precisely control the flow rate to each of the multiple feedpoints relative to the other feedpoints. In particular, there exists a need to uniformly deliver a slurry catalyst composition to each of multiple feed points in a polymerization reactor.